From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 43C93C433B4 for ; Mon, 19 Apr 2021 06:50:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1658B61165 for ; Mon, 19 Apr 2021 06:50:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231465AbhDSGuv (ORCPT ); Mon, 19 Apr 2021 02:50:51 -0400 Received: from szxga04-in.huawei.com ([45.249.212.190]:16599 "EHLO szxga04-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231556AbhDSGur (ORCPT ); Mon, 19 Apr 2021 02:50:47 -0400 Received: from DGGEMS409-HUB.china.huawei.com (unknown [172.30.72.59]) by szxga04-in.huawei.com (SkyGuard) with ESMTP id 4FNy6q6WWqz16LBl; Mon, 19 Apr 2021 14:47:31 +0800 (CST) Received: from [10.174.178.5] (10.174.178.5) by DGGEMS409-HUB.china.huawei.com (10.3.19.209) with Microsoft SMTP Server id 14.3.498.0; Mon, 19 Apr 2021 14:49:48 +0800 Subject: Re: [PATCH v2 5/5] mm/shmem: fix shmem_swapin() race with swapoff To: "Huang, Ying" CC: , , , , , , , , , , , , References: <20210417094039.51711-1-linmiaohe@huawei.com> <20210417094039.51711-6-linmiaohe@huawei.com> <87r1j7kok3.fsf@yhuang6-desk1.ccr.corp.intel.com> From: Miaohe Lin Message-ID: Date: Mon, 19 Apr 2021 14:49:47 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <87r1j7kok3.fsf@yhuang6-desk1.ccr.corp.intel.com> Content-Type: text/plain; charset="windows-1252" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.178.5] X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021/4/19 10:15, Huang, Ying wrote: > Miaohe Lin writes: > >> When I was investigating the swap code, I found the below possible race >> window: >> >> CPU 1 CPU 2 >> ----- ----- >> shmem_swapin >> swap_cluster_readahead >> if (likely(si->flags & (SWP_BLKDEV | SWP_FS_OPS))) { >> swapoff >> si->flags &= ~SWP_VALID; >> .. >> synchronize_rcu(); >> .. > > You have removed these code in the previous patches of the series. And > they are not relevant in this patch. Yes, I should change these. Thanks. > >> si->swap_file = NULL; >> struct inode *inode = si->swap_file->f_mapping->host;[oops!] >> >> Close this race window by using get/put_swap_device() to guard against >> concurrent swapoff. >> >> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") > > No. This isn't the commit that introduces the race condition. Please > recheck your git blame result. > I think this is really hard to find exact commit. I used git blame and found this race should be existed when this is introduced. Any suggestion ? Thanks. > Best Regards, > Huang, Ying > >> Signed-off-by: Miaohe Lin >> --- >> mm/shmem.c | 6 ++++++ >> 1 file changed, 6 insertions(+) >> >> diff --git a/mm/shmem.c b/mm/shmem.c >> index 26c76b13ad23..936ba5595297 100644 >> --- a/mm/shmem.c >> +++ b/mm/shmem.c >> @@ -1492,15 +1492,21 @@ static void shmem_pseudo_vma_destroy(struct vm_area_struct *vma) >> static struct page *shmem_swapin(swp_entry_t swap, gfp_t gfp, >> struct shmem_inode_info *info, pgoff_t index) >> { >> + struct swap_info_struct *si; >> struct vm_area_struct pvma; >> struct page *page; >> struct vm_fault vmf = { >> .vma = &pvma, >> }; >> >> + /* Prevent swapoff from happening to us. */ >> + si = get_swap_device(swap); >> + if (unlikely(!si)) >> + return NULL; >> shmem_pseudo_vma_init(&pvma, info, index); >> page = swap_cluster_readahead(swap, gfp, &vmf); >> shmem_pseudo_vma_destroy(&pvma); >> + put_swap_device(si); >> >> return page; >> } > . >